1. Field of the Invention
The present invention relates to a water-based ink set for ink-jet recording suitable for reducing graininess in a low-density printed part, for improving gas resistance, and for extending a color reproduction range. The present invention also relates to an ink-jet recording method using this water-based ink set for ink-jet recording.
2. Description of the Related Art
When a color image is formed by use of an ink-jet recording method, a three-color ink set has been generally used which is composed of a yellow ink (Y), a magenta ink (M) and a cyan ink (C). Alternatively, a four-color ink set has also been used in which a black ink (K) is further added to the three-color ink set.
Generally, in an ink-jet recording method, the gradation of an image is controlled by adjusting the density of dots formed by ejecting ink onto a recording material. However, when the gradation is controlled by such a method, the dot density decreases in a low-density printed part. Relative to this, the individual dots become easily discernable to the eye, thereby causing a problem that the image is grainy.
In view of the above, a method has been proposed in which two or more inks are employed as cyan ink (see Japanese Patent Application Laid-Open No. H01-95093). In this method, these inks have different dye concentrations and are composed of different kinds of dyes. In addition, a dye which is excellent in vividness but inferior in light fastness is employed in a dark color ink, and a dye which is excellent in light fastness but inferior in vividness is employed in a light color ink. Moreover, a similar method has been proposed for magenta ink (see Japanese Patent Application Laid-Open No. H02-127482). According to these methods, graininess can be improved, but a problem remains that a color reproduction range cannot be extended. Further, when dye ink is employed, color fading first occurs in a low-density printed part, and thus only the low-density printed part becomes whitish to cause the overall image balance to be lost. Therefore, gas resistance, particularly ozone resistance, of a printed part is important.
Generally, in a three-color ink set composed of yellow, magenta and cyan inks, and also in a four-color ink set in which a black ink is added to the three-color ink set, blue color is developed by use of the cyan ink and the magenta ink. When these two inks are used to develop blue color as above, a problem arises that sharp printing quality and vivid color development are difficult to achieve due to a landing error of superposition. A similar problem arises when green color is developed by use of the cyan ink and the yellow ink.